The present invention provides apparatus retro-fittable to existing aircraft to collect data indicating when scheduled maintenance is needed.
Regular scheduled maintenance is mandated for a variety of aircraft equipment and components in the interest of safe operation. One of the most significant aircraft subsystems is an engine, which is subjected to varying levels of stress during the takeoff, climb, cruise, descent and landing segments of a flight. Most engine manufacturers, and the United States' Federal Aviation Administration, rate the service life of an engine according to a schedule that takes account of both the total number of cruise hours of operation and the number of flight cycles.
Historically, most aircraft engines have been maintained in accordance with run time and flight cycle data kept in hand-written logbooks. Such records are subject to both human error (which can result in a premature overhaul) and to deceit, which can be motivated by the high cost of overhauling an engine.
For several decades aviation specialists have pursued the development of systems for automated logging of flight operations. The resultant Airborne Integrated Data Systems have been built into large commercial transport aircraft and have provided requisite maintenance data, although not in a way that has proven to be cost effective in general aviation. These AID systems are commonly characterized by a large number of transducers, a complex wiring network for communicating with these transducers, and a central controller. Installation of these systems is most economically performed at the time of original manufacture of the aircraft, because of the need to run a network of wires, cables or optical fibers throughout the entire airframe. Notable among AID systems are:
Miller et al in U.S. Pat. No. 4,729,102, who teach a system integrable with flight recorders required on some aircraft. Miller et al's system measures a wide variety of engine (e.g. combustion pressures), flight (e.g. altitude) and airframe (e.g. "weight-on-wheels") parameters and also accepts manual data (e.g. takeoff weight). Their system provides out-of-range alarms and detailed operational data. Elapsed flight time and flight cycles are calculable from data their system logs.
Hertzberg et al, in U.S. Pat. No. 5,023,791, and Brooks et al in U.S. Pat. No. 5,111,402, provide teaching on the use of complex aircraft data acquisition systems and of associated ground-based automatic test equipments used during maintenance.
Lawrence et al., in U.S. Pat. No. 5,033,010, disclose an aircraft engine monitoring system in which a computer memory module is permanently attached to a monitored engine. Engine operating data are stored in the memory module by a physically separate engine control unit. Permanently associating the EEPROM data storage device with the engine ensures that a lifetime data log can be maintained in permanent association with the engine even if the engine is moved to a different aircraft or if the engine control unit is changed.
Simpler systems to monitor engine operation and indicate required maintenance are found in the automotive art. Notable among these is U.S. Pat. No. 5,060,156, wherein Vajgart et al teach a system indicating when to change the oil in an engine sump. Vajgart et al's system, when applied to a modern automobile with a computer that controls the engine, uses additional software, but requires the addition of no hardware other than an oil temperature sensor.